The present invention relates to a disc access control method and apparatus, and more particularly to a method and an apparatus, including a cache memory, which are suitable for control of the degeneration of a disc access function due to errors and for recovery of the disc access function.
In a conventional disc control apparatus, having a cache, frequently accessed data is stored in the cache and is read from the cache, without access to a disc, to improve the efficiency of accessing data. As described in Japanese Patent Publication JP-A-60-79447, if a problem in the cache is detected for any one of the storage paths, the whole cache is disconnected and all reading/writing of data in the cache via other storage paths is discontinued. By disconnecting the whole cache, the storage path, which can no longer correctly read/write in the cache, directly updates records on the disc, while other access paths, which can correctly read/write in the cache, are prevented from reading old data from the records in the cache, thereby preventing transfer of old data, which is different from the latest data stored on the disc (hereinafter referred to as a data change condition).
In the conventional disc control apparatus, if any one of the storage paths detects a problem within the cache, the error is regarded as an error in the whole cache, and the cache is disconnected from the disc control apparatus. However, an error on the side of the storage path may appear as a cache error, in which case the cache is disconnected, although there may be many remaining storage paths which can be used to read/write in the cache correctly. Therefore, the usability of the cache is greatly reduced.
A method is conceivable in which a storage path in which a cache error has been detected is closed and the use of the cache by another storage path which can be used to correctly read/write in the cache is continued to be used, thereby increasing the usability of the cache and preventing a data change condition from occurring. However, according to this method, the direct access to a disc by a storage path, in which a cache error has been detected, is also discontinued. Therefore, if there is a disc connected to only the access path in which the cache error has been detected, it will not be possible to access that disc at all.
On the other hand, if a disc is accessed directly, a different data transfer path is used, depending on whether data to be accessed is present in the cache, so that even those storage paths, which have experienced an error in accessing the cache, can access the disc. Therefore, there is the problem that the storage paths are not utilized effectively.